Compressor Having Oil-Level Sensing System

ABSTRACT

A compressor may include a shell containing a motor, a compression mechanism and a lubricant sump. The compressor may also include first and second temperature sensors, and a control module. The first temperature sensor may be at least partially disposed within the lubricant sump and may measure a first temperature of a lubricant at a first position. The second temperature sensor may be at least partially disposed within the lubricant sump and may measure a second temperature of the lubricant at a second position that is vertically higher than the first position. The control module is in communication with the first and second temperature sensors. The control module may determine a first difference between the first temperature and the second temperature. The control module may determine whether a liquid level of the lubricant in the lubricant sump is below a predetermined level based on the first difference.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/130,493 filed on Apr. 15, 2016, which claims the benefit of IndianPatent Application No. 1706MUM2015, filed on Apr. 29, 2015. The entiredisclosures of the applications referenced above are incorporated hereinby reference.

FIELD

The present disclosure relates to a compressor assembly having anoil-level sensing system.

BACKGROUND

This section provides background information related to the presentdisclosure and is not necessarily prior art.

A climate-control system such as, for example, a heat-pump system, arefrigeration system, or an air conditioning system, may include a fluidcircuit having an outdoor heat exchanger, an indoor heat exchanger, anexpansion device disposed between the indoor and outdoor heatexchangers, and one or more compressors circulating a working fluid(e.g., refrigerant or carbon dioxide) between the indoor and outdoorheat exchangers. Efficient and reliable operation of the one or morecompressors is desirable to ensure that the climate-control system inwhich the one or more compressors are installed is capable ofeffectively and efficiently providing a cooling and/or heating effect ondemand.

Effective and efficient operation of a compressor often requireslubricating certain moving components within the compressor.Accordingly, often a compressor will include a lubricant sump orreservoir and lubrication monitoring system, such as a gauge and/orsensor, to monitor the level or quantity of lubricant in the lubricantreservoir. While known lubrication monitoring systems have provenacceptable for their intended purpose, a continuous need for improvementin the relevant art remains. In this regard, it may be desirable toprovide a compressor having a lubricant-level sensing system that canmore effectively and accurately monitor the quantity of lubricant withinthe compressor.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

In one form, a compressor is provided. The compressor may include ashell, a first temperature sensor, a second temperature sensor, and acontrol module. The shell may include a motor, a compression mechanismand a lubricant sump. The first temperature sensor may be at leastpartially disposed within the shell and configured to measure a firsttemperature of a lubricant at a first position. The second temperaturesensor may be at least partially disposed within the shell andconfigured to measure a second temperature of the lubricant at a secondposition that is vertically higher than the first position. The controlmodule may be in communication with the first and second temperaturesensors and configured to determine a first difference between the firsttemperature and the second temperature. The control module may beconfigured to determine whether a liquid level of the lubricant in thelubricant sump is below a predetermined level based on the firstdifference.

In some configurations, a vertical height of the second position isequal to a vertical height of the predetermined level.

In some configurations, the predetermined level equals a minimumacceptable vertical height of said lubricant.

In some configurations, the compressor includes a third temperaturesensor at least partially disposed within the shell and configured tomeasure a temperature of the working fluid at a third position that isvertically higher than the first and second positions. The controlmodule may be configured to determine a second difference between thesecond temperature of the lubricant and the temperature of the workingfluid at the third temperature sensor. The control module may beconfigured to determine whether the vertical height of the lubricant isbelow the second position based on the second difference.

In some configurations, the shell defines a suction chamber containingthe working fluid that is drawn into the compression mechanism forcompression during operation of the compressor. The third temperaturesensor may be disposed within the suction chamber.

In some configurations, the compressor includes a pressure sensordisposed at least partially within the shell vertically above thepredetermined level. The control module may determine whether the liquidlevel is below the predetermined level based on data from the pressuresensor.

In some configurations, the compressor includes a pressure sensordisposed at least partially within the shell. The control module maydetermine whether the liquid level is below the predetermined levelbased on whether data from the pressure sensor indicates a presence ofliquid working fluid in the shell.

In some configurations, the control module determines whether the liquidlevel is below the predetermined level based on whether the compressoris on or off.

In some configurations, the compressor includes a heating elementconfigured to heat liquid within the lubricant sump. The control modulemay determine whether the liquid level is below the predetermined levelbased on whether the heating element is functioning.

In another form, a compressor is provided. The compressor may include ashell, a suction inlet, a fluid path, a first temperature sensor, asecond temperature sensor, and a control module. The shell may include amotor, a compression mechanism, a lubricant sump, and a suction chamber.The suction inlet may extend through the shell and be configured todeliver suction gas to the suction chamber. The fluid path may beconfigured to deliver suction gas. The fluid path may include a firstend terminating proximate the lubricant sump and a second endterminating proximate the suction inlet. The first temperature sensormay be disposed within the fluid path adjacent the first end. The secondtemperature sensor may be disposed within the shell at a positionvertically higher than the first sensor. The control module may be incommunication with the first and second temperature sensors. The controlmodule may determine a temperature difference between the firsttemperature sensor and the second temperature sensor. The control modulemay determine a liquid level in the lubricant sump based on thetemperature difference.

In some configurations, the compressor includes a baffle. The fluid pathmay be at least partially defined by the baffle and the shell.

In some configurations, the first temperature sensor is at leastpartially disposed between the baffle and the shell.

In some configurations, the second temperature sensor is disposedvertically higher than the second end.

In some configurations, the fluid path is disposed externally to theshell.

In some configurations, the working fluid is drawn into the compressionmechanism for compression therein during operation of the compressor.The second temperature sensor may be disposed within the suction chamberand measure a temperature of the working fluid disposed within thesuction chamber.

In some configurations, the liquid level is below the predeterminedlevel when the liquid level is vertically below the first temperaturesensor.

In some configurations, the first temperature sensor is exposed to aflow of the suction gas in a first mode of operation, and the firsttemperature sensor is exposed to a lubricant in a second mode ofoperation.

In yet another form, a method of monitoring a quantity of a lubricantwithin a compressor is provided. The method may include determining afirst temperature from a first temperature sensor at a first locationwithin the compressor. The method may also include determining a secondtemperature from a second temperature sensor at a second location withinthe compressor. The method may further include determining a firstdifference between the first and second temperatures. The method mayadditionally include determining a third temperature from a thirdtemperature sensor at a third location within the compressor. The methodmay also include determining a second difference between the second andthird temperatures and determining whether a liquid level in a lubricantsump within the compressor is below a predetermined level based on atleast one of the first difference and the second difference.

In some configurations, the second location within the compressor isvertically higher than the first location within the compressor.

In some configurations, the method also includes determining a firststandard deviation of measurements from one of the first and secondtemperature sensors. Determining whether the liquid level is below thepredetermined level may be based on the first standard deviation.

In some configurations, the method also includes determining a secondstandard deviation of measurements from the other of the first andsecond temperature sensors. Determining whether the liquid level isbelow the predetermined level may be based on the second standarddeviation.

In some configurations, the method also includes determining first andsecond ratios. The first ratio may be a ratio of the difference betweenthe first and second temperature measurements to the first standarddeviation. The second ratio may be a ratio of the difference between thefirst and second temperature measurements to the second standarddeviation. Determining whether the liquid level is below thepredetermined level may be based on a comparison of the first and secondratios.

In some configurations, the method may also include continuously orintermittently recalculating the first and second ratios, storing valuesof the first and second ratios, and determining whether the liquid levelis falling based on whether the stored values of the first ratio areconverging toward the stored values of the second ratio.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1A is a schematic representation of a compressor having alubricant-level sensing system according to the principles of thepresent disclosure.

FIG. 1B is a schematic representation of another compressor havinglubricant-level sensing system according to the principles of thepresent disclosure.

FIG. 2 is a flowchart illustrating a method for operating thelubricant-level sensing system of FIGS. 1A and/or 1B.

FIG. 3A is a partial cross-sectional view of another compressor having alubricant-level sensing system according to the principles of thepresent disclosure, and illustrating a first lubricant level.

FIG. 3B is a partial cross-sectional view of the compressor of FIG. 3A,and illustrating a second lubricant level.

FIG. 4A is a partial cross-sectional view of yet another compressorhaving a lubricant-level sensing system according to the principles ofthe present disclosure, and illustrating a first lubricant level.

FIG. 4B is a partial cross-sectional view of the compressor of FIG. 4A,and illustrating a second lubricant level.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference tothe accompanying drawings. Example embodiments are provided so that thisdisclosure will be thorough, and will fully convey the scope to thosewho are skilled in the art. Numerous specific details are set forth suchas examples of specific components, devices, and methods, to provide athorough understanding of embodiments of the present disclosure. It willbe apparent to those skilled in the art that specific details need notbe employed, that example embodiments may be embodied in many differentforms and that neither should be construed to limit the scope of thedisclosure. In some example embodiments, well-known processes,well-known device structures, and well-known technologies are notdescribed in detail.

With reference to FIG. 1A, a compressor 10 is provided that may includea shell assembly 12, a motor 14, a compression mechanism 16, a firsttemperature sensor assembly 18, a second temperature sensor assembly 20,a third temperature sensor assembly 22, a pressure sensor 23, and acontrol module 24. As will be explained in more detail below, accordingto the principles of the present disclosure, the compressor 10 isconfigured to determine a level or quantity of a lubricant in thecompressor 10 using at least two of the first, second, and thirdtemperature sensor assemblies 18, 20, 22. In particular, in someconfigurations, the compressor 10 is configured to determine the levelor quantity of lubricant in the compressor 10 using the first, second,and third temperature sensor assemblies 18, 20, 22. In otherconfigurations, the compressor 10 is configured to determine the levelor quantity of lubricant in the compressor 10 using the first and thirdtemperature sensor assemblies 18, 22. Accordingly, while the compressor10 is generally described herein as including first, second, and thirdtemperature sensor assemblies 18, 20, 22, it will be appreciated that insome configurations the compressor 10 may include only two of the first,second, and third temperature sensor assemblies 18, 20, 22.

The shell assembly 12 may include a base 26, a cylindrical shell 28extending along a longitudinal axis A1, and an end cap 30. The shell 28and the base 26 may define a suction chamber 32. The end cap 30 maydefine a discharge chamber 34. A partition 36 may separate the suctionchamber 32 from the discharge chamber 34. A suction port or fitting 38may extend through the shell 28 and communicate with the suction chamber32. A discharge fitting 40 may extend through the end cap 30 andcommunicate with the discharge chamber 34.

The base 26 and shell 28 may define a lubricant sump 42 containing avolume of lubricant (e.g., oil or a mixture of oil and refrigerant) at alubricant level 44. A vertical height of the lubricant level 44 (i.e.,the volume of lubricant in the lubricant sump 42) may vary duringoperation of the compressor 10. A crankcase heater 45 may be disposed inthe lubricant sump 42 and may be operable to heat the lubricant withinthe lubricant sump 42 and/or heat other components of the compressor 10.The control module 24 may be in communication with the crankcase heater45 and may control operation of the crankcase heater 45 to maintain thelubricant in the lubricant sump 42 at or above a predeterminedtemperature.

The compression mechanism 16 may be disposed within the shell assembly12 and may be driven by the motor 14. The compression mechanism 16 maybe any type of compression mechanism, such as a scroll, reciprocating,rotary vane or screw type compression mechanism, for example. Duringoperation of the compression mechanism 16, working fluid from thesuction chamber 32 may be drawn into the compression mechanism 16 andcompressed therein. Compressed working fluid may be discharged from thecompression mechanism 16 into the discharge chamber 34 before exitingthe compressor 10 though the discharge fitting 40.

The first temperature sensor assembly 18 may include a first temperaturesensor 46 and a first casing or slosh guard 48. A further discussion ofthe first temperature sensor assembly 18, including variousconfigurations and functions of the first temperature sensor 46 and thefirst slosh guard 48, may be found in commonly-owned U.S. patentapplication Ser. No. 14/470,234 filed on Aug. 27, 2014 and entitled“Compressor Assembly with Liquid Sensor”, which is hereby incorporatedby reference in its entirety.

The first temperature sensor assembly 18 may be mounted to any suitablestructure to fix the first temperature sensor assembly 18, including thefirst temperature sensor 46, relative to the shell assembly 12 in aposition so that the first temperature sensor 46 is disposed at a firstvertical height H1 above the base 26 of the shell assembly 12. Forexample, the first temperature sensor assembly 18 could be mounted to alower bearing housing (not shown) that rotatably supports a crankshaft50 driven by the motor 14 or the first temperature sensor assembly 18could be mounted to the shell 28. The first vertical height H1 may be apredetermined vertical height that corresponds to a first predeterminedlubricant level in the lubricant sump 42 (e.g., a height of thelubricant level 44 when a predetermined adequate, or minimum acceptable,level of lubricant is present in the lubricant sump 42).

In some embodiments, wires 84 electrically connected to the firsttemperature sensor 46 may be disposed within a wire harness (not shown)that is attached to or disposed within a stator of the motor 14. Thewires 84 may extend from the stator to a sealed terminal plug assembly(not shown) in electrical communication with the control module 24.

The first temperature sensor 46 may be in communication with the controlmodule 24 and may be or include a thermocouple, a PTC (positivetemperature coefficient) thermistor, an NTC (negative temperaturecoefficient) thermistor and/or a heat pulse sensor, for example, and/orany other temperature-sensing device. As will be subsequently described,the control module 24 may be operable to determine whether the lubricantlevel 44 in the lubricant sump 42 is below the first vertical height H1based on data received from the first temperature sensor 46.

Referring again to FIG. 1A, the second temperature sensor assembly 20may include a second temperature sensor 86 and a second casing or sloshguard 88. The second temperature sensor 86 may be disposed within thesecond slosh guard 88 and may be operable to measure a temperature offluid (gas and/or liquid) to which the second temperature sensor 86 isexposed. A further discussion of the second temperature sensor assembly20, including various configurations and functions of the secondtemperature sensor 86 and the second slosh guard 88, may be found incommonly-owned U.S. patent application Ser. No. 14/470,234, which ishereby incorporated by reference in its entirety.

The second temperature sensor assembly 20 may be mounted to any suitablestructure to fix the second temperature sensor assembly 20 relative tothe shell assembly 12 in a position so that the second temperaturesensor 86 is disposed at a second vertical height H2 above the base 26of the shell assembly 12. For example, the second temperature sensorassembly 20 could be mounted to an upper bearing housing (not shown)that rotatably supports the crankshaft 50 or the second temperaturesensor assembly 20 could be mounted to the shell 28 or to an oil draintube connected to the upper bearing housing. The second vertical heightH2 is vertically higher than the first vertical height H1 and may behigher than a predetermined maximum expected lubricant level in thelubricant sump 42. That is, the second vertical height H2 may be at orabove a height of the lubricant level 44 associated with alubricant-overfill or a lubricant-flood condition, for example.

The second temperature sensor 86 may be in communication with thecontrol module 24 and may be or include a thermocouple, a PTC (positivetemperature coefficient) thermistor, an NTC (negative temperaturecoefficient) thermistor and/or a heat pulse sensor, for example, and/orany other temperature-sensing device. As will be subsequently described,the control module 24 may be operable to determine whether the lubricantlevel 44 in the lubricant sump 42 is below the first vertical height H1based on data received from the second temperature sensor 86.

While the first and second temperature sensor assemblies 18, 20 aredescribed above as including the first and second slosh guards 48, 88,respectively, it will be appreciated that, in some embodiments, only oneof the temperature sensor assemblies 18, 20 may include a slosh guard orneither of the temperature sensor assemblies 18, 20 may include a sloshguard. For example, in some configurations the first and/or secondtemperature sensors 46, 86 may be disposed directly within, and/orattached directly to, the shell 28, without the slosh guards 48, 88.

The third temperature sensor assembly 22 may include a third temperaturesensor 90. The third temperature sensor assembly 22 may be mounted toany suitable structure to fix the third temperature sensor assembly 22relative to the shell assembly 12 in a position so that the thirdtemperature sensor 90 is disposed at a third vertical height H3 abovethe base 26 of the shell assembly 12. In some configurations, the thirdtemperature sensor assembly 22 may be mounted to the base 26 such thatthe third vertical height H3 is equal to zero. Accordingly, it will beappreciated that the third vertical height H3 is vertically lower thanthe first vertical height H1, and may be lower than the firstpredetermined lubricant level in the lubricant sump 42. That is, thethird vertical height H3 may be less than the height of the lubricantlevel 44 associated with a minimum acceptable level of lubricant, forexample.

In some embodiments, wires 92 electrically connected to the thirdtemperature sensor 90 may be disposed within a wire harness (not shown)that is attached to or disposed within the stator of the motor 14. Thewires 92 may extend from the stator to a sealed terminal plug assembly(not shown) in electrical communication with the control module 24.

The third temperature sensor 90 may be in communication with the controlmodule 24 and may be or include a thermocouple, a PTC (positivetemperature coefficient) thermistor, an NTC (negative temperaturecoefficient) thermistor and/or a heat pulse sensor, for example, and/orany other temperature-sensing device. As will be subsequently described,the control module 24 may be operable to determine whether the lubricantlevel 44 in the lubricant sump 42 is below the first vertical height H1based on data received from the third temperature sensor 90.

The pressure sensor 23 may be operable to measure a pressure of workingfluid in the suction chamber 32. The pressure sensor 23 may be mountedto any suitable structure within the shell assembly 12 and may be fixedrelative to the shell assembly 12 in a position so that the pressuresensor 23 is disposed above the predetermined maximum expected lubricantlevel. While the pressure sensor 23 is shown in FIG. 1A as being belowthe second vertical height H2, in some embodiments, the pressure sensor23 could be at or above the vertical height H2. For example, thepressure sensor 23 could be mounted to the upper bearing housing or theshell 28. In some embodiments, the pressure sensor 23 could extendthrough the shell 28, as shown in FIG. 1A. In some embodiments, thepressure sensor 23 could be disposed in a suction line (not shown) thatfluidly couples the suction fitting 38 with a heat exchanger (e.g., anevaporator) of the climate control system in which the compressor 10 isinstalled. In some embodiments, the pressure sensor 23 may be mounted ator below the predetermined maximum expected lubricant level.

The pressure sensor 23 may be in communication with the control module24 and may be or include a force-collector type pressure sensor (e.g., asensor having a diaphragm, piston, bourdon tube or bellow to measurestrain or deflection over an area), a resonant type pressure sensor(sensing changes in resonant frequency to measure changes in fluiddensity), and/or a thermal type pressure sensor (sensing changes inthermal conductivity of a fluid), for example, and/or any otherpressure-sensing device. As will be subsequently described, the controlmodule 24 may be operable to determine whether the lubricant level 44 inthe lubricant sump 42 is below the first vertical height H1 based ondata received from the pressure sensor 23.

As described above, the control module 24 may be in communication withthe first, second, and third temperature sensors 46, 86, 90, thepressure sensor 23, and the crankcase heater 45. The control module 24may also be in communication with and control operation of the motor 14and/or other components of the compressor 10 and/or the climate controlsystem.

As will be described in more detail below, the control module 24, thefirst, second, and/or third temperature sensors 46, 86, 90, the pressuresensor 23, and the crankcase heater 45, including the configuration andplacement thereof, can help provide accurate and cost-effectivemonitoring of the quantity of lubricant within the compressor 10.

With reference to FIG. 1B, another compressor 10 a is illustrated. Thecompressor 10 a is generally similar to the compressor 10, except asotherwise provided herein. The compressor 10 a includes the first andthird temperature sensor assemblies 18, 22. In this regard, thecompressor 10 a does not include the second temperature sensor assembly20.

Referring now to FIG. 2, a method 100 will be described in which thecontrol module 24 may determine whether the lubricant level 44 is belowthe first predetermined lubricant level based on information from thefirst temperature sensor 46, the second temperature sensor 86, the thirdtemperature sensor 90, and/or the pressure sensor 23. For example, insome configurations, the control module 24 may determine whether thelubricant level 44 is below the first vertical height H1 based oninformation from the first temperature sensor 46, the second temperaturesensor 86, the third temperature sensor 90, and/or the pressure sensor23. In other configurations, the control module 24 may determine whetherthe lubricant level 44 is below the first vertical height H1 based oninformation from the first temperature sensor 46, the third temperaturesensor 90, and/or the pressure sensor 23. The sensors 46, 86, 90, 23 maycontinuously or intermittently communicate temperature and pressure datato the control module 24, and the control module 24 may continuously orintermittently determine whether the lubricant level 44 is below thefirst vertical height H1 based on such data.

As previously discussed, in some compressors, the lubricant level 44 inthe lubricant sump 42 may be considered to be adequate if the lubricantlevel 44 is vertically at or above the first vertical height H1 (thatis, the first vertical height H1 may be selected to correspond to achosen minimum level or height of lubricant for a particular compressorand/or application). Therefore, when the lubricant level 44 is above thefirst temperature sensor 46, the first temperature sensor 46 will bemeasuring a temperature of the lubricant in the lubricant sump 42. Whenthe lubricant level 44 is below an adequate level (i.e., below the firstvertical height H1), the first temperature sensor 46 will be exposed toworking fluid in the suction chamber 32. Accordingly, the firsttemperature sensor 46 will measure the temperature of working fluid inthe suction chamber 32 when the lubricant level 44 is below an adequatelevel. In some scenarios, notwithstanding the fact that the firsttemperature sensor 46 may be above the lubricant level 44, the firsttemperature sensor 46 may be exposed to the lubricant through splashingor other similar effects caused by movement of the compressor 10.Accordingly, in some scenarios the first temperature sensor 46 maymeasure a temperature of the lubricant even when the first temperaturesensor 46 is above the lubricant level 44.

During normal operation of the compressor 10, the temperature of thelubricant in the lubricant sump 42 may be greater than the temperatureof the working fluid in the suction chamber 32. When the compressor 10is not operating or is in a standby mode, the crankcase heater 45 maymaintain the lubricant at a temperature that is above the temperature ofthe working fluid in the suction chamber 32.

The control module 24 may compare a temperature value NTC3 measured bythe third temperature sensor 90 to a temperature value NTC2 measured bythe second temperature sensor 86. If the temperature value NTC3 measureby the third temperature sensor 90 is not greater than the temperaturevalue NTC2 measured by the second temperature sensor 86, then one of aplurality of conditions may be present. A first one of the plurality ofconditions may be that the compressor 10 is not operating (e.g., thecompressor is turned off). A second one of the plurality of conditionsmay be that the compressor 10 is operating under a flood-back condition,whereby a mixture of liquid and vapor working fluid is drawn into thesuction chamber 32 (e.g., as may occur when the climate control systemis switching between heating and cooling modes or switching into or outof a defrost mode). A third one of the plurality of conditions may bethat the lubricant level 44 is below the predetermined adequate level.Using the method 100, the control module 24 may determine which of theplurality of conditions is present and whether the lubricant level 44 isbelow the predetermined adequate level.

If the temperature value NTC3 measured by the third temperature sensor90 is greater than the temperature value NTC2 measured by the secondtemperature sensor 86, then one of a further plurality of conditions maybe present. A first one of the further plurality of conditions may bethat the lubricant level 44 is at or above the first predeterminedlubricant level (e.g., H1). A second one of the further plurality ofconditions may be that the lubricant level 44 is below the firstpredetermined lubricant level (e.g., H1) and the first temperaturesensor 46 is being exposed to other high temperature sources, such aslubricant sloshing or splashing, as described above.

At 110 of the method 100, the control module 24 may determine whetherthe temperature value NTC3 measured by the third temperature sensor 90is equal to the temperature value NTC2 measure by the second temperaturesensor 86. If the temperature value NTC3 is equal to or approximatelyequal to the temperature value NTC2, the control module 24 may determineat 120 if the compressor 10 is operating. As described above, thecontrol module 24 may control operation of the motor 14, and therefore,the control module 24 may determine whether the motor 14 is operatingbased on control feedback and/or whether the motor 14 is receivingelectrical current. If the control module 24 determines at 120 that thecompressor 10 is not operating, the control module 24 may determine at130 whether the crankcase heater 45 is operating or whether it isfunctional (e.g., by determining if the crankcase heater 45 is receivingelectrical current). If the control module 24 determines that thecrankcase heater 45 is not functional or is not operating, the controlmodule 24 may generate a warning at 140 indicating a fault with thecrankcase heater 45. The warning may be in the form of an audible and/orvisual alarm on the compressor 10 and/or a warning or fault signal sentto a remote protection, control and/or diagnostic system for thecompressor 10 and/or the climate control system, for example. Thewarning generated at 140 may also advise a person to visually check thelubricant level 44 (e.g., through a lubricant level sight glass).

If, at 130, the control module 24 determines that the crankcase heater45 is operating correctly and the crankcase heater 45 has been operatingfor at least a predetermined time period (e.g., a long enough time toallow the crankcase heater 45 to warm the lubricant within the lubricantsump 42), the control module 24 may determine that the lubricant level44 is below the predetermined adequate level at 150. At 155 the controlmodule 24 may then generate a warning and/or shutdown the compressor 10.The warning may be in the form of an audible and/or visual alarm on thecompressor 10 and/or a warning or fault signal sent to a remoteprotection, control and/or diagnostic system for the compressor 10and/or the climate control system, for example. The warning at 155 mayalso advise a person to add lubricant and/or perform service on thecompressor 10 and/or the climate control system.

If, at 120, the control module 24 determines that the compressor 10 isoperating, the control module 24 may determine at 160 that thecompressor 10 is operating under a flood-back condition and/or thelubricant level 44 is below the predetermined adequate level. At 165 thecontrol module 24 may acquire pressure data from the pressure sensor 23.At 170 the control module 24 may determine whether data from thepressure sensor 23 and/or data from the second temperature sensor 86indicate a liquid flood-back condition by comparing the measured valueswith predetermined ranges of values that are known to indicate aflood-back condition for a particular compressor, refrigerant,refrigerant blend and/or climate control system. If the data from thepressure sensor 23 and/or data from the second temperature sensor 86 donot indicate a liquid flood-back condition, the control module 24 maydetermine at 150 that the lubricant level 44 is below the predeterminedadequate level. Then, at 155 the control module 24 may generate thewarning described above and/or shutdown the compressor 10. If the datafrom the pressure sensor 23 and/or data from the second temperaturesensor 86 indicate a liquid flood-back condition at 170, the controlmodule 24 may, at 180, take steps to alleviate or correct the flood-backcondition. The steps to alleviate or correct the flood-back conditioncould include changing a control setting for the compressor 10 (e.g.,changing a capacity of the compressor) and/or a control setting for theclimate control system (e.g., changing condenser fan and/or evaporatorfan speeds, changing timing, amount and/or duration that an expansionvalve is open or closed). After 180, the control module 24 may loop backto 110.

If, at 110, the control module 24 determines that the temperature valueNTC3 is not equal to the temperature value NTC2, the control module 24may, at 190, determine if a temperature value NTC1 measured by the firsttemperature sensor 46 is greater than the temperature value NTC2 by morethan a first predetermined difference Δ1. In some embodiments, the firstpredetermined difference Δ1 may be about ten degrees Fahrenheit, forexample. The first predetermined difference Δ1 can be any value chosento suit a particular compressor, refrigerant, refrigerant blend and/orapplication. If the control module 24 determines at 190 that thetemperature value NTC1 is not greater than the sum of the temperaturevalue NTC2 and the first predetermined difference Δ1, then the controlmodule 24 may repeat steps 160, 170, 150 and 155, as described above, orrepeat steps 160, 170 and 180, as described above.

If, at 190, the control module 24 determines that the temperature valueNTC1 is greater than the sum of the temperature value NTC2 and the firstpredetermined difference Δ1, then the control module 24 may, at 200,determine whether the temperature value NTC1 is greater than thetemperature value NTC3 by more than a second predetermined differenceΔ2. In some embodiments, the second predetermined difference Δ2 may beabout five degrees Fahrenheit, for example. The second predetermineddifference Δ2 can be any value chosen to suit a particular compressor,refrigerant, refrigerant blend and/or application. As discussed above,in some configurations, the compressor 10 a may include the first andthird temperature sensors 46, 90. Accordingly, in some configurationsthe method 100 may begin at 200.

If the control module 24 determines at 200 that the temperature valueNTC1 is not greater than the sum of the temperature value NTC3 and thesecond predetermined difference Δ2, then the control module 24 maydetermine at 210 that the lubricant level 44 is at or above thepredetermined adequate level (i.e., at or above the first verticalheight H1). If the control module 24 determines at 200 that thetemperature value NTC1 is greater than the sum of the temperature valueNTC3 and the second predetermined difference Δ2, then the control module24 may determine at 220 that the lubricant level 44 is below thepredetermined adequate level (i.e., below the first vertical height H1).At 230 the control module 24 may then generate a warning and/or shutdownthe compressor 10. The warning may be in the form of an audible and/orvisual alarm on the compressor 10 and/or a warning or fault signal sentto a remote protection, control and/or diagnostic system for thecompressor 10 and/or the climate control system, for example. Thewarning at 230 may also advise a person to add lubricant and/or performservice on the compressor 10 and/or the climate control system.

With reference to FIGS. 3A and 3B, a portion of another compressor 10 bis provided. The structure and function of the compressor 10 b may besimilar or identical to that of the compressor 10 apart from anyexceptions described below and/or shown in the Figures. Therefore, thestructure and/or function of similar features will not be describedagain in detail.

The compressor 10 b may include a working fluid guide assembly 300. Theworking fluid guide assembly 300 may define a fluid flow path 302 in thesuction chamber 32. In some configurations the shell 28 and the workingfluid guide assembly 300 may define the fluid flow path 302therebetween. The fluid flow path 302 may include an inlet 304 and anoutlet 306. As will be explained in more detail below, the inlet 304 maybe in fluid communication with, and receive suction gas from, thesuction port 38. As illustrated, the first temperature sensor 46 may beadjacent the outlet 306. In some configurations, the first temperaturesensor 46 may be disposed within the fluid flow path 302. Specifically,the first temperature sensor 46 may be disposed between the shell 28 andthe working fluid guide assembly 300 in a radially extending direction.Accordingly, in some configurations, the first temperature sensor 46 maybe arranged to detect a temperature of suction gas received from thesuction port 38 and the fluid flow path 302, as will be explained inmore detail below. The second temperature sensor 86 may be disposed atthe second vertical height H2. In this regard, the second temperaturesensor 86 is exposed to suction gas received from the suction port 38.In particular, in some configurations, the second vertical height H2 maysubstantially equal a vertical height of the suction port 38.

The inlet 304 of the working fluid guide assembly 300 may be disposed ata fourth vertical height H4 above the base 26, and the outlet 306 of theworking fluid guide assembly 300 may be disposed at a fifth verticalheight H5 above the base 26. The fifth vertical height H5 may be lowerthan the fourth vertical height H4. The fourth vertical height H4 may besuch that the inlet 304 is aligned or otherwise in fluid communicationwith the suction port 38. The fifth vertical height H5 may be such thatthe outlet 306 is aligned with, or slightly less than, the firstvertical height H1 of the first temperature sensor 46. In this regard,the fifth vertical height H5 may correspond to the height of thelubricant level 44 when a predetermined threshold or minimum acceptablelevel of lubricant is present in the lubricant sump 42.

As illustrated in FIG. 3A, the working fluid guide assembly 300 mayinclude a deflector 310 and a baffle 312. The deflector 310 and/or thebaffle 312 may define, at least in part, the fluid flow path 302. Inthis regard, while the working fluid guide assembly 300 is described andillustrated herein as including the deflector 310 and/or the baffle 312,it will be appreciated that, in some configurations, the working fluidguide assembly 300 may include a tube or conduit (not shown) definingthe fluid flow path 302.

The deflector 310 may be aligned with the inlet 304 and may include adeflection surface 314 having an arcuate shape facing the suction port38. In this regard, the deflection surface 314 may define a concaveconfiguration in a direction extending along the axis A1 of the shell28, and a convex configuration in a direction extending about the axisA1 of the shell 28. Accordingly, the deflection surface 314 isconfigured to direct a portion of the working fluid from the suctionport 38 downward through the fluid flow path 302 and toward thelubricant sump 42. The deflector 310 may be secured to the compressor 10b in any suitable manner. For example, the deflector 310 could bemounted to the shell 28 and/or to the motor 14.

The baffle 312 may include a first or upper end 318 aligned with thedeflector 310 and a second or lower end 320 aligned with, or otherwisedefining, the outlet 306 of the fluid flow path 302. In someconfigurations, the baffle 312 may include a guiding surface 322 facingthe shell 28. The guiding surface 322 may define an arcuate shape havinga planar configuration in a direction extending along the axis A1 of theshell 28, and a convex configuration in a direction extending about theaxis A1 of the shell 28. Accordingly, the guiding surface 322 isconfigured to direct a portion of the working fluid from the deflector310 downward through the fluid flow path 302 toward the lubricant sump42. The baffle 312 may be secured to the compressor 10 b in any suitablemanner. For example, the deflector 310 could be mounted to the shell 28,the deflector 310, and/or to the motor 14. In some configurations, thedeflector 310 may be integrally and/or monolithically formed with thebaffle 312.

The fluid flow path 302, including the configuration of the workingfluid guide assembly 300 and the placement of the first temperaturesensor 46 relative to the fluid flow path 302, can help provide accurateand cost-effective monitoring of the quantity of lubricant within thecompressor 10 b. Specifically, with reference to FIG. 3A, during a firstoperating scenario the lubricant level 44 in the lubricant sump 42 maybe higher or greater than the predetermined threshold or minimumacceptable level (e.g., H1) of lubricant. Accordingly, during the firstoperating scenario, the temperature value NTC1 measured by the firsttemperature sensor 46 may correspond to a temperature of the lubricantin the lubricant sump 42.

With reference to FIG. 3B, during a second operating scenario thelubricant level 44 in the lubricant sump 42 may be lower or less thanthe predetermined threshold or minimum acceptable level of lubricant.Accordingly, during the second operating scenario, the temperature valueNTC1 may correspond to a temperature of the working fluid in the suctionchamber 32. In this regard, as the compressor 10 b operates in thesecond scenario, the working fluid guide assembly 300 can direct theworking fluid through the fluid flow path 302 and over the firsttemperature sensor 46, such that the first temperature sensor 46 sensesa temperature of the working fluid. In this regard, the flow of workingfluid through the fluid flow path 302 can also help to prevent thelubricant from contacting first temperature sensor 46. Specifically, adownward force F1 produced by the flow of working fluid through thefluid flow path 302 can offset an upward force F2 produced by sloshed orsplashed portions of the lubricant, such that the splashed portions ofthe lubricant do no contact the first temperature sensor 46 when thecompressor 10 b is operating in the second scenario.

With reference to FIGS. 4A and 4B, another compressor 10 c is provided.The structure and function of the compressor 10 c may be similar oridentical to that of the compressor 10 b apart from any exceptionsdescribed below and/or shown in the Figures. Therefore, the structureand/or function of similar features will not be described again indetail. In addition, like reference numerals are used hereinafter and inthe drawings to identify like components, while like reference numeralscontaining letter extensions (i.e., “c”) are used to identify thosecomponents that have been modified.

The compressor 10 c may include a working fluid guide assembly 300 cdefining a fluid flow path 302 c. As illustrated, in some configurationsat least a portion of the fluid flow path 302 c may extend outside ofthe shell 28 and the suction chamber 32. It will be appreciated,however, that the fluid flow path 302 c may extend inside the suctionchamber 32 within the scope of the present disclosure. The fluid flowpath 302 c may include an inlet 304 c and an outlet 306 c. The inlet 304c may be disposed at a fourth vertical height H4 c, and the outlet 306 cmay be disposed at a fifth vertical height H5 c that is lower than thefourth vertical height H4 c. The fourth vertical height H4 c may be suchthat the inlet 304 c is aligned, or otherwise in fluid communication,with the suction port 38. In this regard, as illustrated in FIG. 4A theinlet 304 c may be in communication with the suction port 38 at alocation outside of the shell 28. The fifth vertical height H5 c may besuch that the outlet 306 c is aligned with the first vertical height H1of the first temperature sensor 46. In this regard, the fifth verticalheight H5 c may correspond to the height of the lubricant level 44 whena predetermined threshold or minimum acceptable level of lubricant ispresent in the lubricant sump 42. As illustrated, the first temperaturesensor 46 may be adjacent the outlet 306 c. In some configurations, thefirst temperature sensor 46 may be disposed within the fluid flow path302 c.

As illustrated in FIG. 4A, the working fluid guide assembly 300 c mayinclude a tube or conduit 410 defining at least a portion of the fluidflow path 302 c. The conduit 410 may include a vertically extendingportion 412 and a horizontally extending portion 414. In this regard,the vertically extending portion 412 may extend in a directionsubstantially parallel to the axis A1 of the shell 28, and thehorizontally extending portion 414 may extend in a directionsubstantially perpendicular to the axis A1 of the shell 28. Thevertically extending portion 412 may include or otherwise define theinlet 304 c, such that the vertically extending portion 412 is coupledto, or otherwise in fluid communication with, the suction port 38. Thehorizontally extending portion 414 may include or otherwise define theoutlet 306 c. As illustrated, in some configurations, the horizontallyextending portion 414 may extend through the shell 28, such that thehorizontally extending portion 414 is in fluid communication with thesuction chamber 32. In some configurations, the first temperature sensor46 may be disposed within the horizontally extending portion 414. Theconduit 410, including the vertically and horizontally extendingportions 412, 414, can direct a portion of the working fluid from thesuction port 38 through the fluid flow path 302 c and into communicationwith, or over, the first temperature sensor 46. The conduit 410 may besecured to the suction port 38 and/or the shell 28 in any suitablemanner.

As will be described in more detail below, the fluid flow path 302 c,including the configuration of the conduit 410 and the placement of thefirst temperature sensor 46 relative to the fluid flow path 302 c and/orthe conduit 410, can help provide accurate and cost-effective monitoringof the level and/or quantity of lubricant within the compressor 10 c.Specifically, with reference to FIG. 4A, during a first operatingscenario the lubricant level 44 in the lubricant sump 42 may be higheror greater than the predetermined threshold or minimum acceptable levelof lubricant. Accordingly, during the first operating scenario, thetemperature value NTC1 measured by the first temperature sensor 46 maycorrespond to a temperature of the lubricant in the lubricant sump 42.

With reference to FIG. 4B, during a second operating scenario thelubricant level 44 in the lubricant sump 42 may be lower or less thanthe predetermined threshold or minimum acceptable level of lubricant.Accordingly, during the second operating scenario, the temperature valueNTC1 can correspond to a temperature of the working fluid in the suctionchamber 32. In this regard, as the compressor 10 c operates in thesecond scenario, the working fluid guide assembly 300 c can direct theworking fluid through the fluid flow path 302 c and over the firsttemperature sensor 46. The flow of working fluid through the fluid flowpath 302 c can help to prevent the lubricant from contacting firsttemperature sensor 46. Specifically, a force F1 c produced by the flowof working fluid through the fluid flow path 302 c can offset a force F2c produced by the sloshed or splashed portions of the lubricant, suchthat the splashed portions of the lubricant do no contact the firsttemperature sensor 46 when the compressor 10 c is operating in thesecond scenario.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

In this application, including the definitions below, the term ‘module’may be replaced with the term ‘circuit.’ The term ‘module’ may refer to,be part of, or include: an Application Specific Integrated Circuit(ASIC); a digital, analog, or mixed analog/digital discrete circuit; adigital, analog, or mixed analog/digital integrated circuit; acombinational logic circuit; a field programmable gate array (FPGA); aprocessor circuit (shared, dedicated, or group) that executes code; amemory circuit (shared, dedicated, or group) that stores code executedby the processor circuit; other suitable hardware components thatprovide the described functionality; or a combination of some or all ofthe above, such as in a system-on-chip.

The module may include one or more interface circuits. In some examples,the interface circuits may include wired or wireless interfaces that areconnected to a local area network (LAN), the Internet, a wide areanetwork (WAN), or combinations thereof. The functionality of any givenmodule of the present disclosure may be distributed among multiplemodules that are connected via interface circuits. For example, multiplemodules may allow load balancing. In a further example, a server (alsoknown as remote, or cloud) module may accomplish some functionality onbehalf of a client module.

The term code, as used above, may include software, firmware, and/ormicrocode, and may refer to programs, routines, functions, classes, datastructures, and/or objects. The term shared processor circuitencompasses a single processor circuit that executes some or all codefrom multiple modules. The term group processor circuit encompasses aprocessor circuit that, in combination with additional processorcircuits, executes some or all code from one or more modules. Referencesto multiple processor circuits encompass multiple processor circuits ondiscrete dies, multiple processor circuits on a single die, multiplecores of a single processor circuit, multiple threads of a singleprocessor circuit, or a combination of the above. The term shared memorycircuit encompasses a single memory circuit that stores some or all codefrom multiple modules. The term group memory circuit encompasses amemory circuit that, in combination with additional memories, storessome or all code from one or more modules.

The term memory circuit is a subset of the term computer-readablemedium. The term computer-readable medium, as used herein, does notencompass transitory electrical or electromagnetic signals propagatingthrough a medium (such as on a carrier wave); the term computer-readablemedium may therefore be considered tangible and non-transitory.Non-limiting examples of a non-transitory, tangible computer-readablemedium are nonvolatile memory circuits (such as a flash memory circuit,an erasable programmable read-only memory circuit, or a mask read-onlymemory circuit), volatile memory circuits (such as a static randomaccess memory circuit or a dynamic random access memory circuit),magnetic storage media (such as an analog or digital magnetic tape or ahard disk drive), and optical storage media (such as a CD, a DVD, or aBlu-ray Disc).

The apparatuses and methods described in this application may bepartially or fully implemented by a special purpose computer created byconfiguring a general purpose computer to execute one or more particularfunctions embodied in computer programs. The functional blocks andflowchart elements described above serve as software specifications,which can be translated into the computer programs by the routine workof a skilled technician or programmer.

The computer programs include processor-executable instructions that arestored on at least one non-transitory, tangible computer-readablemedium. The computer programs may also include or rely on stored data.The computer programs may encompass a basic input/output system (BIOS)that interacts with hardware of the special purpose computer, devicedrivers that interact with particular devices of the special purposecomputer, one or more operating systems, user applications, backgroundservices, background applications, etc.

The computer programs may include: (i) descriptive text to be parsed,such as HTML (hypertext markup language) or XML (extensible markuplanguage), (ii) assembly code, (iii) object code generated from sourcecode by a compiler, (iv) source code for execution by an interpreter,(v) source code for compilation and execution by a just-in-timecompiler, etc. As examples only, source code may be written using syntaxfrom languages including C, C++, C#, Objective C, Haskell, Go, SQL, R,Lisp, Java®, Fortran, Perl, Pascal, Curl, OCaml, Javascript®, HTML5,Ada, ASP (active server pages), PHP, Scala, Eiffel, Smalltalk, Erlang,Ruby, Flash®, Visual Basic®, Lua, and Python®.

None of the elements recited in the claims are intended to be ameans-plus-function element within the meaning of 35 U.S.C. §112(f)unless an element is expressly recited using the phrase “means for,” orin the case of a method claim using the phrases “operation for” or“for.”

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting. As usedherein, the singular forms “a,” “an,” and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. The terms “comprises,” “comprising,” “including,” and“having,” are inclusive and therefore specify the presence of statedfeatures, integers, s, operations, elements, and/or components, but donot preclude the presence or addition of one or more other features,integers, s, operations, elements, components, and/or groups thereof.The method s, processes, and operations described herein are not to beconstrued as necessarily requiring their performance in the particularorder discussed or illustrated, unless specifically identified as anorder of performance. It is also to be understood that additional oralternative s may be employed.

When an element or layer is referred to as being “on,” “engaged to,”“connected to,” or “coupled to” another element or layer, it may bedirectly on, engaged, connected or coupled to the other element orlayer, or intervening elements or layers may be present. In contrast,when an element is referred to as being “directly on,” “directly engagedto,” “directly connected to,” or “directly coupled to” another elementor layer, there may be no intervening elements or layers present. Otherwords used to describe the relationship between elements should beinterpreted in a like fashion (e.g., “between” versus “directlybetween,” “adjacent” versus “directly adjacent,” etc.). As used herein,the term “and/or” includes any and all combinations of one or more ofthe associated listed items.

Although the terms first, second, third, etc. may be used herein todescribe various elements, components, regions, layers and/or sections,these elements, components, regions, layers and/or sections should notbe limited by these terms. These terms may be only used to distinguishone element, component, region, layer or section from another region,layer or section. Terms such as “first,” “second,” and other numericalterms when used herein do not imply a sequence or order unless clearlyindicated by the context. Thus, a first element, component, region,layer or section discussed below could be termed a second element,component, region, layer or section without departing from the teachingsof the example embodiments.

Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,”“lower,” “above,” “upper,” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. Spatiallyrelative terms may be intended to encompass different orientations ofthe device in use or operation in addition to the orientation depictedin the figures. For example, if the device in the figures is turnedover, elements described as “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the example term “below” can encompass both an orientation ofabove and below. The device may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein interpreted accordingly.

What is claimed is:
 1. A compressor comprising: a shell including amotor, a compression mechanism and a lubricant sump; a first temperaturesensor at least partially disposed within said lubricant sump andconfigured to measure a first temperature of a lubricant at a firstposition; a second temperature sensor at least partially disposed withinsaid lubricant sump and configured to measure a second temperature ofsaid lubricant at a second position that is vertically higher than saidfirst position; and a control module in communication with said firstand second temperature sensors, said control module configured todetermine a first difference between the first temperature and thesecond temperature, said control module configured to determine whethera liquid level of said lubricant in said lubricant sump is below apredetermined level based on said first difference.
 2. The compressor ofclaim 1, wherein a vertical height of said second position is equal to avertical height of said predetermined level.
 3. The compressor of claim1, wherein said predetermined level equals a minimum acceptable verticalheight of said lubricant.
 4. The compressor of claim 1, furthercomprising a third temperature sensor at least partially disposed withinsaid shell and configured to measure a temperature of working fluid at athird position that is vertically higher than said first and secondpositions, wherein said control module is configured to determine asecond difference between the second temperature of said lubricant andthe temperature of said working fluid at said third temperature sensor,said control module configured to determine whether a vertical height ofsaid lubricant is below said second position based on said seconddifference.
 5. The compressor of claim 4, wherein said shell defines asuction chamber containing said working fluid that is drawn into saidcompression mechanism for compression therein during operation of thecompressor, and wherein said third temperature sensor is disposed withinsaid suction chamber.
 6. The compressor of claim 1, further comprising apressure sensor disposed at least partially within said shell verticallyabove said predetermined level, wherein said control module determineswhether said liquid level is below said predetermined level based ondata from said pressure sensor.
 7. The compressor of claim 1, furthercomprising a pressure sensor disposed at least partially within saidshell, wherein said control module determines whether said liquid levelis below said predetermined level based on whether data from saidpressure sensor indicates a presence of liquid working fluid in saidshell.
 8. The compressor of claim 1, wherein said control moduledetermines whether said liquid level is below said predetermined levelbased on whether the compressor is on or off.
 9. The compressor of claim1, further comprising a heating element configured to heat liquid withinsaid lubricant sump, and wherein said control module determines whethersaid liquid level is below said predetermined level based on whethersaid heating element is functioning.
 10. The compressor of claim 1,further comprising a fluid path for delivering suction gas, the fluidpath having a first end proximate said lubricant sump and a second endproximate a suction inlet extending through said shell,
 11. Thecompressor of claim 10, wherein said first temperature sensor isdisposed within said fluid path adjacent said first end.
 12. Thecompressor of claim 11, wherein said fluid path is at least partiallydefined by said shell and a baffle disposed within said shell.
 13. Amethod comprising: determining a first temperature from a firsttemperature sensor at a first location within a compressor; determininga second temperature from a second temperature sensor at a secondlocation within said compressor; determining a first difference betweensaid first and second temperatures; determining a third temperature froma third temperature sensor at a third location within said compressor;determining a second difference between said second and thirdtemperatures; and determining whether a liquid level in a lubricant sumpwithin said compressor is below a predetermined level based on at leastone of said first difference and said second difference.
 14. The methodof claim 13, wherein said second location within said compressor isvertically higher than said first location within said compressor. 15.The method of claim 13, further comprising determining a first standarddeviation of measurements from one of said first and second temperaturesensors, wherein determining whether said liquid level is below saidpredetermined level is based on said first standard deviation.
 16. Themethod of claim 13, further comprising directing suction gas along afluid path having a first end proximate said lubricant sump and a secondend proximate a suction inlet of said compressor.
 17. The method ofclaim 16, wherein said first temperature sensor is disposed within saidfluid path adjacent said first end.
 18. The method of claim 17, whereinsaid fluid path is defined by a shell of said compressor and a baffledisposed within said shell.
 19. The method of claim 13, furthercomprising determining a pressure from a pressure sensor disposed atleast partially within a shell of said compressor at a fourth locationvertically above said predetermined level; and determining whether saidliquid level in said lubricant sump is below said predetermined levelbased on said pressure.
 20. The method of claim 13, further comprisingdetermining whether a heating element for said lubricant sump isfunctioning; and determining whether said liquid level in said lubricantsump is below said predetermined level based on whether said heatingelement is functioning.